CoSb3 is a highly important host-guest material for the engineering of high-performance thermoelectric materials.[1] Its crystal structure has empty cavities and when guest atoms are added to CoSb3, its thermoelectric properties are greatly enhanced due to decreased thermal conductivity.[2] In order to understand the origin of the thermoelectric properties of this family of materials, it is important to understand the crystal structure and chemical bonding of the un-doped host material.[3] This can be achieved through analysis of the charge density, which in principle can be obtained from modeling of accurate X-ray diffraction data.[4] However, considering the heavy elements, the high symmetry and the perfect crystallinity of this inorganic network structure one cannot think of a much more challenging case for experimental charge density analysis. In the present study we analyze several low-temperature experimental X-ray diffraction data sets collected at different sources using different experimental conditions. These are compared with high-level ab-initio periodic DFT calculations. The results clearly show that in the current study the data obtained from synchrotron sources were superior to data obtained from conventional sources. Some important experimental requirements are that the data need to be collected on a high-intensity, high-energy source using very small crystals so as to diminish extinction and absorption effects. The data collected at SPring8 seem to fulfill these requirements most satisfactorily.[5] References [1] D.T. Morelli et al., Phys. Rev. B 51 (1995) 9622. [2] J.-L. Mi, M. Christensen, E. Nishibori, B.B. Iversen. Phys. Rev. B 84 (2011) 064114. [3] T. Caillat, A. Borshchevsky, J.-P. Fleurial. J. Appl. Phys. 80 (1996) 4442-4449. [4] A. Ohno et al., Phys. Rev. B 76 (2007) 064119. [5] M. Schmøkel, L. Bjerg, F.K. Larsen, J. Overgaard, S. Cenedese, M. Christensen, G.K.H. Madsen, C. Gatti, A. Pinkerton, E. Nishibori, K. Sugimoto, M. Takata, B.B. Iversen. In preparation.